Extracellular adenosine triphosphate protects oxidative stress-induced increase of p21WAF1/Cip1 and p27Kip1 expression in primary cultured renal proximal tubule cells: Role of PI3K and Akt signaling

Oxidative stress, the result of cellular production of reactive oxygen species (ROS), has been implicated in causing many renal diseases. Adenosine triphosphate (ATP) is an important extracellular signal in the regulation of many intracellular processes in normal tubular cells as well as in the pathogenesis of cell injury. This study investigated the effect of ATP onH2O2-induced increase of cyclin kinase inhibitors (CKI) expression and its related signal molecules in primary cultured renal proximal tubule cells (PTCs). H2O2 inhibited DNA synthesis in a concentration- (>50 mM) and time-dependent manner (>2 h), as determined by thymidine and BrdU incorporation, and by increase in the p21WAF/Cip1 and p27Kip1 expression levels. In contrast, ATP increased the level of thymidine, BrdU incorporation (>10 5 M), and decreased the p21WAF/Cip1 and p27Kip1 expression levels, suggesting that ATP has a protective effect againstH2O2-induced oxidative damage. Suramin, reactive blue 2 (RB-2), MRS 2159, and MRS 2179 did block the reversing effect of ATP. In addition, AMP-CPP or 2-methylthio-ATP blockedH2O2-induced inhibition ofDNA synthesis, suggesting all these P2 purinoceptors may be potentially involved. ATP-induced stimulation of DNA synthesis was blocked by phosphatidylinositol 3-kinase (PI3K) and Akt inhibitors. These results suggest the involvement of P2 purinoceptors-mediated PI3K/Akt signal pathway in the protective effect of ATP againstH2O2-induced oxidative damage. Indeed, pre-treatment with PI3K or Akt inhibitors did not protect H2O2-induced lipid peroxide (LPO) production and inhibition of thymidine incorporation. In conclusion, ATP, in part, blocked H2O2-induced increase of p21WAF1/Cip1 and p27Kip1 expression through PI3K and Akt signal pathway in renal PTCs.This research was supported by the Research Project on the Production of Bio-organs (No. 200503010301) Ministry of Agriculture and Forestry and the authors acknowledge a graduate fellowship provided by the Ministry ofEducation andHuman ResourcesDevelopment through the Brain Korea 21 project, Republic of Korea